1. Field of the Invention
The present invention relates to a hot-runner molding apparatus and a hot-runner nozzle in injection molding for injecting a molten resin into a cavity by a hot runner to provide a molded article such as an optical element.
2. Description of the Related Art
In general, an optical element made of a resin functions as a small lens for use in, for example, a digital camera, an endoscope, a microscope, or a mobile phone. Such an optical element made of a resin is generally molded by injection molding. Recently, in order to reduce the impact on the environment and decrease waste material given that resin material used for optical elements is more expensive than materials used for general constituent components, the optical element is molded by using a hot runner. Since the hot runner sends a molten resin injected from an injection molding machine into a cavity through a resin channel maintained at a high temperature, an amount of material in the resin channel that ends up as waste material can be reduced. Therefore, at present, various forms of hot runners are suggested from many manufacturers.
Jpn. Pat. Appln. KOKAI Publication No. H07-232353 discloses, for example, an open torpedo-type hot runner. In this open torpedo-type hot runner, a torpedo portion arranged at a tip of a hot-runner nozzle is heated at a central portion of a nozzle hole portion. The nozzle hole portion is provided in a molding die and cools a resin. Therefore, the resin at the nozzle tip has high fluidity controllability, and thus a dripping or stringing phenomenon when the nozzle is enlarged, or a gate clogging phenomenon that prevents injection by clogging the gate with the resin when the nozzle is made smaller, hardly occurs. Therefore, this hot runner is suitable for molding precision components requiring strict external appearance quality or strict form accuracy. Furthermore, the molten resin is sent to a position near the nozzle tip through one channel, and branches to a plurality of hole portions at the nozzle tip. As a result, a pipeline resistance of the resin channel is reduced, and the resin can be injected using low pressure.
An end tip having a nozzle can be replaced with respect to a tip holder. Due to such replacement, the shape of the tip can be changed due to changing a resin or a product shape, and it has been proposed that a channel area can also be changed. In the replacement, the tip holder has a screw hole portion into which the end tip is fitted. Moreover, the end tip has a male screw portion that is formed at a proximal end portion of the end tip and screwed into the screw hole portion.